The purpose of this research is to make some suggestions, based on social science findings, for legal reform on stepfamily. First, this reseach provides a overview of the current state of the law in Japan and the United States of America as it applies to stepfamilies in four areas child support obligation during the marriage and after the termination of the remarriage, custody rights of stepparents during the marriage and after the termination of the remarriage, visitation rights of stepparents after divorce, and intestacy statutes as they apply to stepfamilies. The review demonstrates how the presumption of the current law differs from the social science findings about the relationships within stepfamilies. Namely, legislatures and courts in both country have not generally recoginized the stepparent-stepchild relationship as one that Is potentially enduring beyond the marriage of the biological parent and stepparent. In contrast, empirical research has assessed the quality of stepparent-stepchild relationship and has identified those stepchildren who are most likely to have positive relationships with stepparents. Further, social science findings suggest that the lack of clarity about roles in stepfamilies may exacerbate adjustment difficulties. Consequently this reseach concludes that stepparents who have meaningful relationships with their stepchildren should have the same rights and obligations as do biological parents and that lawmakers should probe the social science findings regarding stepfamilies to better tailor the law to the expectations and realities of stepfamilies.